The invention relates to an immersion measuring probe, particularly a drop-in measuring probe for metal melts. The probe has a measuring head on which at least one sensor carrier with at least one sensor is arranged, and the sensor carrier is held at or in an opening of the measuring head.
Measuring probes of this type are known, for example, from German Patent DE 198 49 433 C1. Drop-in measuring probes are thrown from a certain height from a holder into a molten metal. The measuring head mounted at one end of a carrier tube is generally made of steel in order to provide the mass required to penetrate the slag layer built up on molten steel or iron. Inside the carrier tube a signal cable is wound up, which is connected with a measurement system and which unwinds from the carrier tube during the fall into the molten metal. In the measuring head a sensor carrier having at least one sensor is arranged, for example a temperature sensor or an electrochemical element for measurement of the oxygen content of the molten metal. When penetrating the slag layer lying on top of the molten steel, slag may adhere to the measuring head. This slag adhering to the measuring head, and perhaps to the protective cap of the sensors, can influence the measurement of the properties of the molten steel and lead to measurement errors.
Besides the contact of their solid electrolyte material with the molten metal, electrochemical sensors also need a so-called bath contact between their so-called counter electrode and the molten metal. The bath contact is often achieved outside the measuring probe via signal lines to the molten metal (See German Patent DE 30 21 949 C2), or, as described for example in German published patent application Nos. DE 195 31 661 A1 or DE 196 52 596 A1, as an additional component which itself must be correspondingly protected. These publications, however, do not relate to drop-in measuring probes and are not suitable for the particular mechanical loads (particularly shock loads) of such probes.
A sensor unit is known from German published patent application No. DE 102 03 121 A1, in which a sensor carrier is located at a measuring head, wherein the sensor carrier has a sensor and wherein the measuring head is in electrical contact with parts of the sensor. A similar sensor is known from European published patent application EP 363 616 A2. Further, a solid electrolyte tube is known from German Patent DE 101 03 701 C1, which is used in a measurement system for the determination of oxygen in molten metals. The solid electrolyte tube is closed on its backside end with a locking cap.